This document specifies a measurement method based on an automatic method for determination of the mass concentration of formaldehyde in ducts and stacks emitting to the atmosphere. It specifies the sampling and gas conditioning system. Furthermore, it specifies the characteristics to be determined and the performance criteria to be fulfilled by portable automated measuring systems (P-AMS) using appropriate techniques to measure formaldehyde. This method is intended for intermittent monitoring of formaldehyde emissions as well as for the calibration and validation of automated formaldehyde measuring systems. The analyser is calibrated using test gases produced by a test gas generator.